Disconnect the power from the unit and then disconnect the fan and use an Ohmmeter to test the fan motor to check that it has continuity. Also check that the fan blades spin freely when operated by hand.
If the fan motor is open circuit then the Kenwood part number for the fan motor assembly is T49-0025-02. A quick search online using the part number, gave no results for suppliers. You may have better luck.
Are the any markings on the fan itself, such as make and model number which may be of further help (if it is not made by Kenwood and has no markings)?
If the fan motor tests OK with the Ohmmeter, then here’s a link to the service manual for the receiver which may be of some help. Clicking on the link will download the manual directly to your computer.
There is a protection circuit for the fan which you can test to see whether it shows that the fan is OK or not.
Here’s an image taken from the manual that shows this.
(click on image to enlarge for better viewing)